In recent years, servers, supercomputers, and other electronic equipment have become faster in speed and higher in performance. Along with this, the amount of heat generated by the electronic devices built into the electronic equipment (for example, central processing units (CPUs)) at the time of operation has been increasing. In general, servers and other such electronic equipment include a plurality of electronic devices. The amount of heat generated by these is tremendous. Further, if the heat generated by the electronic devices causes the inside of the electronic equipment to become high in temperature, the electronic equipment will be impaired in function and breakdown of the electronic equipment will be caused. Therefore, to maintain the functions of electronic devices and avoid breakdown of the electronic equipment, it is necessary to cool the heat generating electronic devices. As a device for cooling an electronic device, a cooler called a “cooling plate” which is arranged with its main body in contact with the electronic device and runs a coolant through the inside of the main body to cool the electronic device is known. The coolant which is raised in temperature after cooling the electronic device is cooled by a cooling device which is provided at the outside of the cooler and is then refluxed to the cooler.
As such a cooler, a cooler which cools a semiconductor module provided with a plurality of semiconductor devices built in a power conversion device and a jet type cooler having a plurality of headers for cooling a power electronic device are known. Further, a channel distribution type cooler is also known.
In this regard, most of the coolers up to now have been structured to be supplied with coolant raised in temperature at the downstream side of the coolant flow, so there has been the problem of the temperature of a downstream side semiconductor module becoming higher.
As opposed to this, a channel distribution type cooler is divided into channels through which the coolant before cooling the heat generating member flows (distribution paths) and a channel through which the coolant after cooling the heat generating member flows (collection path) and is high in cooling efficiency of the heat generating member. Here, using FIG. 1 to FIG. 6, a channel distribution type cooler (below, referred to as a “cooling plate”) will be explained.
FIG. 1 illustrates a standalone apparatus 90 which is provided with air-cooling systems and liquid cooling systems of the comparative art. In a liquid cooling system which cools cooling plates, a cooling system jointly using an air-cooling system is built in. At the front side of the standalone apparatus 90, a plurality of CPU units 91 provided with liquid cooling systems are mounted. The CPU units 91 are supplied with coolant from a coolant cooling device 30 provided separately from the standalone apparatus 90. On the other hand, at the back side of the standalone apparatus 90, air-cooling system use fans 92, 93 are provided.
FIG. 2A illustrates the layout of an air-cooling system 94 and a liquid cooling system 80 in a CPU unit 91 mounted in the standalone apparatus 90 illustrated in FIG. 1. A circuit board 96 of a CPU unit 91 has memory devices 95 and concealed CPUs and interface devices. The memory devices 95 are cooled by the cooling air CW of the air-cooling system 94. The liquid cooling system 80 has cooling plates 83 for cooling the CPUs and cooling plates 84 for cooling interface devices and is connected through coolant piping 82 (coolant feed pipes 82A and coolant recovery pipes 82B) to a coolant inlet 81 and a coolant outlet 85. The coolant inlet 81 and the coolant outlet 85 are connected to the coolant cooling device 30 illustrated in FIG. 1A.
FIG. 2B explains the cooling operation of the air-cooling system 94 and the liquid cooling system 80 in the CPU unit 91 illustrated in FIG. 2A. In the air-cooling system 94, memory devices 95 provided on the circuit board 96 are cooled by the cooling air CW, while the coolant piping 82 of the liquid cooling system 80 is arranged in a direction perpendicular to the flow of cooling air CW. The coolant piping 82 connected to the coolant inlet 81 is provided with a coolant feed pipes 82A arranged from one end to the other end of the circuit board 96 and coolant recovery pipes 82B folded back at the other end and returning to the coolant outlet 85. In this example, two systems of the coolant feed pipes 82A and the coolant recovery pipes 82B are respectively provided.
In the middle of each coolant feed pipe 82A, a plurality of cooling plates 83 for cooling the CPUs and a plurality of cooling plates 84 for cooling the interface devices are provided, but nothing is provided in the middle of each coolant recovery pipe 82B. Coolant entering from the coolant inlet 81 runs through the coolant feed pipes 82A and flows successively through the plurality of cooling plates 83 to cool the CPUs, then flows successively through the plurality of cooling plates 84 to cool the interface devices, then runs through the coolant recovery pipes 83B and is returned to the coolant outlet 85.
FIG. 3 illustrates the structure of a cooling plate 20 of one example of the cooling plates 83 and 84 illustrated in FIG. 2A. The cooling plate 20 is provided with a main body 21 sealed by a top plate 22. On the top plate 22, there are a coolant inflow pipe 23 provided with a coolant inlet 23A connected to a coolant feed pipe 82A illustrated in FIGS. 2A and 2B and a coolant outflow pipe 24 provided with a coolant outlet 24A connected to a coolant recovery pipe 82B. The cooling plate 20 is placed with its main body 21 sitting on a heat generating device 97 mounted on the circuit board 96 and absorbs heat generated by the heat generating device 97 to thereby remove heat from the heat generating device 97.
FIG. 4 illustrates the structure of the inside of the main body 21 when taking off the top plate 22 of the cooling plate 20 illustrated in FIG. 3 to which the coolant inflow pipe 23 and the coolant outflow pipe 24 are attached. The inside of the main body 21 is divided by a later explained separating wall 5 into an upper space 10 and a lower space not illustrated in FIG. 4. At the inside of the upper space 10, there is a first channel and a second channel partitioned by a partition wall 25. The first channel is provided with a first coolant storage part 11 storing the coolant flowing in from the coolant inflow pipe 23 and a coolant distribution path 13 guiding the coolant in the first coolant storage part 11 in the direction of the coolant outflow pipe 24 and running it through the through holes 26 provided in the separating wall 5 to flow to the lower space. The second channel has a coolant collection path 14 which runs a coolant returning from the lower space through the through holes 26 provided in the separating wall 5 in the direction of the coolant outflow pipe 24 and a second coolant storage part 12 which stores the coolant flowing in from the coolant collection path 14 and sends it out to the coolant outflow pipe 24. The coolant returning from the lower space through the through holes 26 is coolant after absorbing the heat of the heat generating member at the lower space.
The partition wall 25 partitioning the upper space 10 is of a meandering shape including folded back walls 25A at the first coolant storage part 11 side and folded back walls 25B at the second coolant storage part 12 side. The folded back walls 25A, 25B are connected by parallel side walls 25C. The plurality of coolant distribution paths 13 connected to the first coolant storage part 11 are formed surrounded by the side walls 25C and the inner circumferential surfaces of the folded back walls 25B. At the separating wall 5 forming the bottom surfaces of the coolant distribution paths 13, through holes 26 are formed from the first coolant storage part 11 side toward the inner circumferential surfaces of the folded back walls 25B. The coolant collection paths 14 are formed surrounded by the side walls 25C and the inner circumferential surfaces of the folded back walls 25A, while the separating wall 5 forming the bottom surfaces of the coolant collection paths 14 are formed with through holes 26 from the inner circumferential surface side of the folded back walls 25B toward the second coolant storage part 12. The through holes 26 of this example are provided in straight lines at the center parts of the coolant distribution paths 13 and the bottom surfaces of the coolant collection paths 14, but the through holes 26 need not be straight lines and are not particularly determined in form. The parts with hatching in FIG. 4 are the parts connecting with the bottom surface of the top plate 22.
FIG. 5A illustrates the main body 21 of the first coolant storage part 11 side when cutting along the line A-A the main body 21 from which the top plate 22 of the cooling plate 20 illustrated in FIG. 4 has been removed. FIG. 5A illustrates the lower space 15 provided at the lower side of the upper space 10 by the separating wall 5. In the lower space 15, coolant flows in through the through holes 26 from the coolant distribution paths 13, passes over the bottom surface 1B of the main body 1, and absorbs the heat generated by a heat generating member under the bottom surface 1B to remove heat from the heat generating member. The coolant absorbing the heat of the heat generating member passes through the through holes 26 and flows in from the lower space 15 to the coolant collection paths 14. Accordingly, the lower space 15 is a heat removing coolant chamber removing the heat of the heat generating member. Below, the lower space 15 will also be described as the “heat removing coolant chamber 15”.
FIG. 5B and FIG. 6 are explanatory views for explaining the flow of coolant in the cooling plate 20. The cooling flowing into the coolant inflow pipe 23 passes through the first coolant storage part 11 and enters the plurality of coolant distribution paths 13. The coolant entering the coolant distribution paths 13 flows along the coolant distribution paths 13 while flowing into the heat removing coolant chamber 15 through the through holes 26 and absorbing the heat generated by a heat generating device (not illustrated) in contact with the bottom surface 21B of the main body 21. The coolant absorbing the heat of the heat generating device runs from the heat removing coolant chamber 15 through the through holes 26 to enter the coolant collection paths 14, flows through the coolant collection paths 14 in the same direction as the coolant flowing through the coolant distribution paths 13, and is collected at the second coolant storage part 12. The coolant collected at the second coolant storage part 12 is drained from the coolant outflow pipe 24 illustrated in FIG. 4 to the outside of the cooling plate 20.
Note that, in the above explained cooling plate 20, the first coolant storage part 11 is a single space to which a plurality of coolant distribution paths 13 are connected. The second coolant storage part 12 is also a single space to which a plurality of coolant collection paths 14 are connected. On the other hand, the first coolant storage part 11 may be partitioned into sections for the individual coolant distribution paths 13 by sectioning walls provided at the outside of the folded back walls 25A of the partition wall 25. Similarly, the second coolant storage part 12 may also be partitioned into sections for the individual coolant collection paths 14 by sectioning walls provided at the outside of the folded back walls 25B of the partition wall 25. Further, in FIG. 5B, the ceiling plate 22 is drawn as a separate member from the main body 21, but the ceiling plate 22 is sometimes formed by the same member as the main body 21 and the overall assembly is called the “main body”.
In this regard, in the channel distribution type cooling plate 20 in the comparative art as well, as illustrated in FIG. 6, the side walls 25C of the partition wall 25 separating the coolant distribution paths 13 and coolant collection paths 14 are warmed by the coolant flowing through the coolant collection paths 14 and take on the heat H. This being so, due to the conduction of heat from the side walls 25C, the coolant flowing through the coolant distribution paths 13 gradually rises in temperature as it flows to the downstream sides of the coolant distribution paths 13. As a result, the heat removing coolant chamber 15 positioned at the downstream part of the coolant distribution paths 13 is supplied with coolant raised in temperature and therefore there is the problem that the heat generating device positioned at the downstream side of the coolant distribution paths 13 becomes higher in temperature.
As a technique for solving this problem, it may be considered to make the partition wall 25 separating the coolant distribution paths 13 and coolant collection paths 14 a material resistant to heat conduction. However, with this technique, there is the problem that the cooling performance of the cooling plate as a whole remarkably falls and the heat removing surface (bottom surface 21B of main body 20) as a whole rises in temperature.